This invention relates to reciprocating engines such as gasoline or diesel internal combustion engines, as well as to Stirling or other external combustion engine. The term engine as used herein is not limited only to prime movers or power sources, but can also be applied to other reciprocating devices such as piston type pumps and compressors.
In a typical reciprocating engine, a piston oscillates within a cylinder, and defines within the cylinder a chamber of variable volume. This chamber has minimum and maximum volumes, respectively, at piston positions corresponding to top dead center, (where the piston is closest to the cylinder head), and to bottom dead center, (where the piston is closest to the crank or other drive linkage).
In a conventional internal combustion engine, a combustion or power stroke normally occurs as the phase of the cycle in which the piston travels from top dead center to bottom dead center. Conversely, a compression stroke occurs on the phase in which the piston travels from bottom dead center to top dead center. In an internal combustion engine, the maximum forces occurring on the power stroke far exceed the maximum forces sustained on the compression stroke. In order to provide more stable and smoother operation, and to reduce internal forces on the drive linkages, it is desirable for the power stroke to occupy other than 180.degree. of crank travel. This would also provide a greater mechanical advantage to the expanding gas within the chamber because of the optimization of rotation angle to the power stroke.
There have been several previous attempts to alter the power stroke by employing toggle linkage systems that connect a piston to a pair of parallel, counter-rotating cranks. Two such systems are described, for example, in U.S. Pat. Nos. 1,585,796 of May 25, 1926, and 2,392,921, of Jan. 15, 1946.
In these previous patented systems, the piston reciprocates on a line perpendicular to a plane defined by the axes of the two cranks. The length of the connecting rods that connect the piston to the crank is proportioned, with respect to the length of the crank and the distance between the two crank shafts, so that the angle between the connecting rods is less than 90.degree. when the piston is at bottom dead center.
While these previous attempts were able to change the crankshaft rotational angle that corresponded to a power stroke, these particular twin-crank drive mechanisms have not proved to be entirely practicable. One reason for this is that there is a high compressive force on the drive linkage, that is, the piston pushes against the connecting rod. The highly elevated compressive forces, especially after combustion on the power stroke, tend to buckle or break the connecting rods, and can also cause heavy wear on the wrist pins where the connecting rods are journalled to the cranks.